City-Tunnel Leipzig - Wannenwetsch HDW

Development and use of project-specific special solutions:

Gutting of the diaphragm wall – City-Tunnel Leipzig

The City-Tunnel Leipzig is reconstructing the regional rail transport at the railway junctions in Leipzig from scratch. The DEGES Deutsche Einheit Fernstraßenplanungs-und bau GmbH was the contractor responsible for the project. An initial study entitled "S-Bahn Leipzig - Citytunnel" was introduced in 1995. The overall commissioning of the City-Tunnel followed in autumn 2013.

Since being commissioned, the City-Tunnel has had positive effects on the capacity of the S-Bahn suburban rail lines in Central Germany.

Job Report - Factsheet

Projevt: City-Tunnel Leipzig
Contractor: DEGES Deutsche Einheit Fernstraßenplanungs- und -bau GmbH
Corporation: ARGE Tunnel- und Ingenieurbau Leipzig LOS B
Type of activity: Gutting of the diaphragm wall
Feature: Working under the impact of pressurised air in the excavating chamber as well as using a special construction

The job

Due to geometric constrictions, only one manufactured seal block could be used in the jet grouting process when waterproofing the station "Markt" ready for the demolition of the excavation diaphragm wall.

Its tightness was impaired further due to deposits of wood and lignite, which is why an internal concrete body including a mechanical pick was concreted in front of the tunnel wall. The solidly reinforced diaphragm wall was demolished under the impact of pressurised air with a specially constructed erosion structure and was then filled with concrete.

Working under pressure

In order to reach the aim of removing 100m3 of concrete within 20 days, it was necessary to work in a 24/7 cycle. Not only did enough staff have to be available for this, but the special requirements for work under the impact of pressurised air had to be taken into consideration (e.g. sufficient time buffer for the work and for specific medical requirements). As well as this, a specially trained doctor monitored the health of the workers around the clock.

The time-consuming inward and outward transfer of man and machine required the utmost care and concentration from the machine operators during their work. Injured workers or damaged material would only have been able to be transported to the surface with great difficulty. This would have caused an immense loss of time.

Technology fact: Use of two aggregates, each consisting of 550 kW including exhaust air concept | Removal of 100 m3 during 20 days

Machine technology

A specially aligned construction was developed so that the solidly reinforced diaphragm wall could be demolished. The double nozzle, cemented on a movable supporting frame, was supplied with 530 litres per minute by two 550 kW aggregates.

Thanks to this, the cement could be removed quickly. The exhaust air system was part of the entire concept and was supplied by the concrete removal firm Wannenwetsch.

Result

Several reinforcement layers had to be blasted and dismantled all together. During this process, 100 m3 of concrete was removed in each of the four construction phases, with each lasting just 20 days.

The pressure of the deadline, the density of the reinforcement and the impact of the pressurised air posed a great challenge for the entire Wannenwetsch team and all those taking part in the build, which could only be fulfilled with up-to-date high-performance technology, a concept designed especially for the project and above all, the high level of personal commitment shown by our workers.

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